: This research program addresses basic questions related to processing of auditory information and recognition of speech by individuals with normal hearing and cochlear hearing loss. An important consequence of the active cochlear mechanism, revealed by studies of basilar-membrane mechanics, is the nonlinearity (compression) in basilar membrane input-output functions. Among the most prominent psychophysical effects of a loss of compression are changes in growth of masking and suppression, and increased effects of time-varying maskers, each of which may diminish speech recognition in noise. Three aims are proposed to address key question concerning the effects of suppression and the benefits of compression and nonlinearities in the peripheral auditory system to speech recognition in noise. Aim 1 assess growth of masking for tonal and speech signals at moderate and high levels to test the hypothesis that compression and other nonlinearites underlie improvements in speech recognition in noise, and that more linear response resulting from cochlear injury expain diminished speech recognition in noise for persons with cochlear hearing loss. Aim 2 test the hypothesis that suppression contributes to normal speech recognition in noise and that a reduction of loss of suppression at high levels or with cochlear hearing loss contributes to declines in speech in noise. Aim 3 measures detection and speech recognition in fluctuating maskers to test the hypothesis that compression and nonlinearities underlie the benefits derived form masker fluctuations and that a loss of compression reduces this benefits for individuals with cochlear hearing loss. A long-term goal is to discover the basis for, and the means for reducing, the detrimental effects of cochlear hearing loss on the perception of speech. A better understanding of these effects is essential if individuals with cochlear hearing loss are to achieve maximum benefit form amplified speech in adverse listening conditions.